Some thermodynamic processes for cooling and heating by adsorption of a refrigerating fluid on a solid adsorbent use zeolite and other sorption materials such as activated carbon and silica gel. In these processes, the thermal energy from adsorbing zeolite in one place is used to heat desorbing zeolite located in another place. U.S. Pat. No. 4,138,850 relates to a system for such solar heat utilization employing a solid zeolite adsorbent mixed with a binder, pressed, and sintered into divider panels and hermetically sealed in containers. U.S. Pat. No. 4,637,218 relates to systems for a heat pump using zeolite as an adsorbent wherein the zeolite is prepared by slicing natural zeolite rock with a carbide saw, or by pressing slightly-wetted, powdered zeolite into bricks. The bricks used in U.S. Pat. No. 4,637,218 are preferably not more than 10 mm in thickness.
U.S. Pat. No. 4,548,046 relates to an apparatus for cooling or heating by adsorption of a refrigerating fluid on a solid adsorbent. The operations employ a plurality of tubes provided with parallel radial fins filled or covered with solid adsorbent such as Zeolite 13X located on the outside of the tubes.
The thermodynamic aspects of developing a zeolite-water adsorption refrigeration unit are well known. An article entitled, "Thermodynamic Analysis of a Solar Zeolite Refrigeration System," by S. Chang and J. A. Roux, which appeared in the Journal of Solar Energy Engineering, August 1985, Volume 107, pages 189-194 provides a discussion of the main parameters, including adsorber properties.
In adsorber/generator based cooling systems the most significant parameter is the overall heat transfer coefficient between the adsorbent bed and the cooling or heating gases per unit weight of adsorbent in the system. This parameter has been related in the literature to the cooling power per kilogram of adsorbent. The higher the cooling power, the more efficient the adsorber/generator system. Current systems are limited by requiring a high adsorbent regenerator temperature or a long cycle time to achieve relatively low cooling power values.
In a paper tided, "Application of Adsorption Cooling System to Automobiles," by Moloyuki Suzuki, presented at the Solid Sorption Refrigeration Symposium--Paris, France, Nov. 18-20, 1992. Suzuki disclosed the results of a study to particularly point out the technological limits associated with the application of adsorption cooling systems to passenger car air conditioning. Suzuki's model considered an adsorbent bed wherein the adsorption step corresponds to the cooling step where water evaporation takes place at a water container, and wherein regeneration step corresponding to a generation step where the adsorbent bed is heated by exhaust gases to desorb the water. These steps are repeated in series requiring at least two units to achieve continuous cooling. Suzuki suggests the use of "quick cycles with a high overall heat transfer coefficient will result in acceptable designs. Currently, overall heat transfer coefficients in the ranges of 25 to 50 are reported in a paper titled, "Reaction Beds for Dry Sorption Machines," by M. Groll and presented at the above mentioned Solid Sorption Refrigeration Symposium. Suzuki predicts a threshold value of 100 kW/m.sup.3 K for overall heat transfer coefficient as a target for the future work, and further points out the need for systems with mechanical strength for use in automobiles, but does not suggest how this value which is greater than 3 times the ability of the current art can be achieved.
U.S. Pat. No. 5,279,359 to Erickson discloses an apparatus and a process for sorption heat pumping using a multiplicity of intermittent cyclic triplex sorption modules. The cyclic triplex sorption modules comprise hermetically sealed tubes, each of which contains at least two solid sorbents and filled with a refrigerant. The preferred refrigerant is ammonia and the solid sorbents are salts such as BaCl.sub.2, SiCl.sub.2, Ca Cl.sub.2, MnCl.sub.2, FeCl.sub.2 and SiBr.sub.2.
U.S. Pat. No. 4,660,629 to Maier-Laxhuber et al. discloses a continuous adsorption cooling device comprising a plurality of adsorption containers filled with adsorbent wherein the adsorption containers are rotated through flow segments which form passageways for a heat carrier stream. The adsorption containers contain an adsorption substance from which an operating substance is extracted by absorbing heat from a heat carrier flow and into which the operating substance is readsorbed, emitting heat to a further heat carrier flow.
Prior methods of using zeolite adsorbents in devices for cooling or heating by adsorption of a refrigerating fluid on a solid adsorbent have been inefficient and difficult to prepare. Those methods of preparation included cutting natural rock into thin bricks and mounting these bricks on to heat exchange surfaces or casting powdered zeolites and mixtures thereof with clays into panels or slabs for direct contact with fluids. Prior devices have sought to minimize heat transfer losses in systems for sorption cooling by employing flat containers filled with adsorbent suspended in heat carrier streams, or their slabs of adsorbent wired or mounted next to heat transfer surfaces. Many of these devices incorporated further flow enhancers such as sorbate conduits, weirs, valves, and wicks to establish maximum contact of the operating fluid and the adsorbent with heat exchange surfaces. Devices are sought which simplify the manufacture of sorption cooling systems and improve the overall system power per unit-mass of sorbent.
It is the object of the instant invention to provide an improved sorption cooling device for use in waste heat recovery and air conditioning systems.
It is a further objective of the instant invention to provide an adsorbent/refrigerant system which provides a high overall efficiency within the limits of typical waste heat recovery and air conditioning cycles.